You need to be able to pay for talent, and often that's antithetical to union philosophy.
My father worked in the retail grocery industry in LA in the '50s and '60s. Always in union shops, and once he'd established himself the never worked for scale. He always negotiated a higher rate and his bosses will willing to negotiate because his reputation was that good. Eventually, he moved up into management, but he kept his union membership for the medical and pension benefits. I might add that as he was now management, he was no longer expected to honor strikes or picket lines and the union never bothered him about it because that was now part of his job.